General code maintenance:
- remove dead code
- remove as many
#defineas possible and useconstexprinstead - remove adafs occurrences and replace with gkfs
- reformat code to unify code style as of CPPCoreGuidelines
- rearrange imports, remove unused imports
- separate cmake configurations and FS configurations
- encapsulate non-prefix gkfs functions into namespaces
- change copyright statement to 2020
Since most code has been merged. This is a good time to tackle this now.